Slot liner materials are used in the stators of electric machines, such as generators and/or motors, to provide insulation between the stator core and the stator windings. In a rotary electrical machine, such as a generator or motor, the slot liner will separate stator windings, placed in the slots of a stator core, from the core. When operating, the slot liner provides electrical insulation of the stator windings from the core, while allowing heat generated in the stator windings due to current, to transfer from the stator windings to the stator core.